Namespace Extension Windows Explorer icons disappear

Hello,

i have a Namespace Extension which works very well so far. All virtual folders. For several different folders, I have about 10 ico in the resource file of my dll. Now from time to time the several icons disappear / vanish and something similar to icon 1 from this here is displayed.

http://fc05.deviantart.net/fs70/f/20...12-d3dndrt.jpg

Do you know what's going wrong?

When I delete the icon cache (iconcache.db) everything works fine, but not for long...mostly after 1-2 restarts or so the icons are gone again.

I've also raised the icon cache without any result.

Kind regards,
Michael